This invention relates to apparatus for electronically generating synchronization pulses for an internal combustion engine.
In an internal combustion engine having a fuel injection system or some other operation which must be synchronized with engine rotation, it is necessary to generate a timing signal identifying the rotational position of the engine for controlling the operation. The timing signal is usually in the form of periodically generated synchronization pulses which occur in relation to the top dead center position of a specified engine cylinder.
In many known systems the synchronization pulses are derived from a voltage signal produced by a detector or sensor which indicates the engine speed and crankshaft position.
For example the synchronization pulses may be derived from the voltage signal produced by a crankshaft transmitter. This voltage signal typically consists of a series of alternate positive and negative pulses generated as the crankshaft rotates, with an additional pulse being generated at a certain reference position, e.g.; the top dead center position of the first cylinder.
In one known system the crankshaft transmitter is placed adjacent a slotted or toothed disc which rotates with the crankshaft. The transmitter produces alternate positive and negative pulses as the teeth pass it. A magnet is provided at the reference position and thus an extra pulse is generated each time the magnet passes the sensor.
The voltage signal from the crankshaft transmitter thus consists of a series of alternate negative and positive pulses with two consecutive pulses of the same sense at regular intervals.
It is possible to generate, from the crankshaft transmitter voltage, a pulse sequence which switches from a first level to a second level in response to a negative going pulse and from the second level to the first level in response to a positive going pulse. This pulse sequence is hereinafter referred to as the negative/positive evaluation signal. This has been achieved using an integrated circuit together with a number of external components and has been used in many hybrid electronic ignition devices. Suitable circuitry for generating such a pulse sequence is described in detail in DE-OS 3208262.
It is desirable to generate the synchronization pulses from the crankshaft transmitter voltage using as little as possible additional circuitry.
In hybrid devices only a limited space can be made available for implementing the circuit. This means that all functions additionally needed must be incorporated into existing or new integrated components. It is obviously advantageous, to incorporate additional functions into existing components wherever possible.
It has been proposed to utilise the circuitry for generating the negative/positive evaluation signal for generating the synchronization pulses. However, the previous proposals have required modifications to the integrated circuit.